This is a proposal to carry out positional cloning of the gene for Margarita Island ectodermal dysplasia (ED4), a rare autosomal recessive disorder which is quite common (1/200) on Isla Margarita in the Caribbean, probably as result of a founder effect from one of the original Spanish settlers. The disease has been mapped by the applicant to a 1-2 Mb interval of chromosome 11q23, and shown to be associated with a common ancestral haplotype. A second aim of the proposal is to determine whether ED4 is allelic to the Zlotogora-Ogur syndrome, a rare disorder reported in three families with phenotypic similarity to ED4. After cloning the ED4 gene, the third aim of the proposal is to determine whether the murine ED4 homologue is responsible for the "rough-fur" murine mutation, making it a mouse model of the human disease. The last aim is to initiate studies to determine the function of the ED4 gene.